Devices and methods for the restoration of a spinal disc

ABSTRACT

A system and method is provided for maintaining a proper intervertebral disc height during the replacement or augmentation of the spinal disc. In one embodiment, a cannulated distractor is used to distract the adjacent vertebrae and maintain a proper disc space height. The cannulated distractor is fluidly connected to a source of fluent material for injection into the disc space. The distraction includes a distraction tip resident within the disc space that includes a central lumen and a number of openings communicating with the lumen to dispense the fluent material within the disc space.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/282,755,filed on Oct. 29, 2002 now U.S. Pat. No. 7,004,945 in the name of thesame inventor, and which claims priority to provisional application Ser.No. 60/336,002, entitled “Devices, Methods and Assemblies forIntervertebral Disc Repair and Regeneration”, and provisionalapplication Ser. No. 60/336,333, entitled “Pretreatment of CartilaginousEndplates Prior to Treatment of the Intervertebral Disc with anInjectable Biomaterial”, both of which were filed on Nov. 1, 2001, andthe disclosure of which are both incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the treatment of spinaldiseases and injuries, and more specifically to the restoration of thespinal disc following surgical treatment. The invention contemplatesdevices and methods for restoring the normal intervertebral disc spaceheight and for facilitating the introduction of biomaterials for use inthe repair and restoration of the intervertebral disc.

The intervertebral disc is divided into two distinct regions: thenucleus pulposus and the annulus fibrosus. The nucleus lies at thecenter of the disc and is surrounded and contained by the annulus. Theannulus contains collagen fibers that form concentric lamellae thatsurround the nucleus and insert into the endplates of the adjacentvertebral bodies to form a reinforced structure. Cartilaginous endplatesare located at the interface between the disc and the adjacent vertebralbodies.

The intervertebral disc is the largest avascular structure in the body.The disc receives nutrients and expels waste by diffusion through theadjacent vascularized endplates. The hygroscopic nature of theproteoglycan matrix of the nucleus operates to generate highintra-nuclear pressure. As the water content in the disc increases, theintra-nuclear pressure increases and the nucleus swells to increase theheight of the disc. This swelling places the fibers of the annulus intension. A normal disc has a height of about 10-15 mm.

There are many causes of disruption or degeneration of theintervertebral disc that can be generally categorized as mechanical,genetic and biochemical. Mechanical damage includes herniation in whicha portion of the nucleus pulposus projects through a fissure or tear inthe annulus fibrosus. Genetic and biochemical causes can result inchanges in the extracellular matrix pattern of the disc and a decreasein biosynthesis of extracellular matrix components by the cells of thedisc. Degeneration is a progressive process that usually begins with adecrease in the ability of the extracellular matrix in the centralnucleus pulposus to bind water due to reduced proteoglycan content. Witha loss of water content, the nucleus becomes desiccated resulting in adecrease in internal disc hydraulic pressure, and ultimately to a lossof disc height. This loss of disc height can cause the annulus to bucklewith non-tensile loading and the annular lamellae to delaminate,resulting in annular fissures. Herniation may then occur as ruptureleads to protrusion of the nucleus.

Proper disc height is necessary to ensure proper functionality of theintervertebral disc and spinal column. The disc serves severalfunctions, although its primary function is to facilitate mobility ofthe spine. In addition, the disc provides for load bearing, loadtransfer and shock absorption between vertebral levels. The weight ofthe person generates a compressive load on the discs, but this load isnot uniform during typical bending movements. During forward flexion,the posterior annular fibers are stretched while the anterior fibers arecompressed. In addition, a translocation of the nucleus occurs as thecenter of gravity of the nucleus shifts away from the center and towardsthe extended side.

Changes in disc height can have both local and global effects. On thelocal (or cellular, level) decreased disc height results in increasedpressure in the nucleus, which can lead to a decrease in cell matrixsynthesis and an increase in cell necrosis and apoptosis. In addition,increases in intra-discal pressure create an unfavorable environment forfluid transfer into the disc, which can cause a further decrease in discheight.

Decreased disc height also results in significant changes in the globalmechanical stability of the spine. With decreasing height of the disc,the facet joints bear increasing loads and may undergo hypertrophy anddegeneration, and may even act as a source of pain over time. Decreasedstiffness of the spinal column and increased range of motion resultingfrom loss of disc height can lead to further instability of the spine,as well as back pain. The outer annulus fibrosus is designed to providestability under tensile loading, and a well-hydrated nucleus maintainssufficient disc height to keep the annulus fibers properly tensioned.With decreases in disc height, the annular fibers are no longer able toprovide the same degree of stability, resulting in abnormal jointmotion. This excessive motion can manifest itself in abnormal muscle,ligament and tendon loading, which can ultimately be a source of backpain.

Radicular pain may result from a decrease in foraminal volume caused bydecreased disc height. Specifically, as disc height decreases, thevolume of the foraminal canal, through which the spinal nerve rootspass, decreases. This decrease may lead to spinal nerve impingement,with associated radiating pain and dysfunction

Finally, adjacent segment loading increases as the disc height decreasesat a given level. The discs that must bear additional loading are nowsusceptible to accelerated degeneration and compromise, which mayeventually propagate along the destabilized spinal column.

In spite of all of these detriments that accompany decreases in discheight, where the change in disc height is gradual many of the illeffects may be “tolerable” to the spine and may allow time for thespinal system to adapt to the gradual changes. However, the suddendecrease in disc volume caused by the surgical removal of the disc ordisc nucleus may heighten the local and global problems noted above.Many disc defects are treated through a surgical procedure, such as adiscectomy in which the nucleus pulposus material is removed. During atotal discectomy, a substantial amount (and usually all) of the volumeof the nucleus pulposus is removed and immediate loss of disc height andvolume can result. Even with a partial discectomy, loss of disc heightcan ensue. Discectomy alone is the most common spinal surgicaltreatment, frequently used to treat radicular pain resulting from nerveimpingement by disc bulge or disc fragments contacting the spinal neuralstructures.

In another common spinal procedure, the discectomy may be followed by animplant procedure in which a prosthesis is introduced into the cavityleft in the disc space when the nucleus material is removed. Thus far,the most prominent prosthesis is a mechanical device or a “cage” that issized to restore the proper disc height and is configured for fixationbetween adjacent vertebrae. These mechanical solutions take on a varietyof forms, including solid kidney-shaped implants, hollow blocks filledwith bone growth material, push-in implants and threaded cylindricalcages.

In more recent years, injectable biomaterials have been more widelyconsidered as an augment to a discectomy. As early as 1962, AlfNachemson suggested the injection of room temperature vulcanizingsilicone into a degenerated disc using an ordinary syringe. In 1974,Lemaire and others reported on the clinical experience of Schulman withan in situ polymerizable disc prosthesis. Since then, many injectablebiomaterials or scaffolds have been developed as a substitute for thedisc nucleus pulposus, such as hyaluronic acid, fibrin glue, alginate,elastin-like polypeptides, collagen type I gel and others. A number ofpatents have issued concerning various injectable biomaterialsincluding: cross-linkable silk elastin copolymer discussed in U.S. Pat.No. 6,423,333 (Stedronsky et al.); U.S. Pat. No. 6,380,154 (Capello etal.); U.S. Pat. No. 6,355,776 (Ferrari et al.); U.S. Pat. No. 6,258,872(Stedronsky et al.); U.S. Pat. No. 6,184,348 (Ferrari et al.); U.S. Pat.No. 6,140,072 (Ferrari et al.); U.S. Pat. No. 6,033,654 (Stedronsky etal.); U.S. Pat. No. 6,018,030 (Ferrari et al.); U.S. Pat. No. 6,015,474(Stedronsky); U.S. Pat. No. 5,830,713 (Ferrari et al.); U.S. Pat. No.5,817,303 (Stedronsky et al.); U.S. Pat. No. 5,808,012 (Donofrio etal.); U.S. Pat. No. 5,773,577 (Capello); U.S. Pat. No. 5,773,249(Capello et al.); U.S. Pat. No. 5,770,697 (Ferrari et al.); U.S. Pat.No. 5,760,004 (Stedronsky); U.S. Pat. No. 5,723,588 (Donofrio); U.S.Pat. No. 5,641,648 (Ferrari); and U.S. Pat. No. 5,235,041 (Capello etal.); protein hydrogel described in U.S. Pat. No. 5,318,524 (Morse etal.); U.S. Pat. No. 5,259,971 (Morse et al.); U.S. Pat. No. 5,219,328(Morse et al.); and U.S. Pat. No. 5,030,215; polyurethane-filledballoons discussed in No. 60/004,710 (Felt et al.); U.S. Pat. No.6,306,177 (Felt et al.); U.S. Pat. No. 6,248,131 (Felt et al.) and U.S.Pat. No. 6,224,630 (Bao et al.); collagen-PEG set forth in U.S. Pat. No.6,428,978 (Olsen et al.); U.S. Pat. No. 6,413,742 (Olsen et al.); U.S.Pat. No. 6,323,278 (Rhee et al.); U.S. Pat. No. 6,312,725 (Wallace etal.); U.S. Pat. No. 6,277,394 (Sierra); U.S. Pat. No. 6,166,130 (Rhee etal.); U.S. Pat. No. 6,165,489 (Berg et al.); U.S. Pat. No. 6,123,687(Simonyi et al.); U.S. Pat. No. 6,111,165 (Berg); U.S. Pat. No.6,110,484 (Sierra); U.S. Pat. No. 6,096,309 (Prior et al.); U.S. Pat.No. 6,051,648 (Rhee et al.); U.S. Pat. No. 5,997,811 (Esposito et al.);U.S. Pat. No. 5,962,648 (Berg); U.S. Pat. No. 5,936,035 (Rhee et al.);and U.S. Pat. No. 5,874,500 (Rhee et al.); chitosan in U.S. Pat. No.6,344,488 to Chenite et al.; a variety of polymers discussed in U.S.Pat. No. 6,187,048 (Milner et al.; recombinant biomaterials in No.60/038,150 (Urry); U.S. Pat. No. 6,004,782 (Daniell et al.); U.S. Pat.No. 5,064,430 (Urry); U.S. Pat. No. 4,898,962 (Urry); U.S. Pat. No.4,870,055 (Urry); U.S. Pat. No. 4,783,523 (Urry et al.); U.S. Pat. No.4,783,523 (Urry et al.); U.S. Pat. No. 4,589,882 (Urry); U.S. Pat. No.4,500,700 (Urry); U.S. Pat. No. 4,474,851 (Urry); U.S. Pat. No.4,187,852 (Urry et al.); and U.S. Pat. No. 4,132,746 (Urry et al.); andannulus repair materials described in U.S. Pat. No. 6,428,576 toHaldimann.

These references disclose biomaterials or injectable scaffolds that haveone or more properties that are important to disc replacement, includingstrong mechanical strength, promotion of tissue formation,biodegradability, biocompatibility, sterilizability, minimal curing orsetting time, optimum curing temperature, and low viscosity for easyintroduction into the disc space. The scaffold must exhibit thenecessary mechanical properties as well as provide physical support. Itis also important that the scaffold be able to withstand the largenumber of loading cycles experienced by the spine. The biocompatibilityof the material is of utmost importance. Neither the initial materialnor any of its degradation products should elicit an unresolved immuneor toxicological response, demonstrate immunogenicity, or expresscytoxicity.

Generally, the above-mentioned biomaterials are injected as viscousfluids and then cured in situ. Curing methods include thermosensitivecross-linking, photopolymerization, or the addition of a solidifying orcross-linking agent. The setting time of the material is important—itshould be long enough to allow for accurate placement of the biomaterialduring the procedure yet should be short enough so as not to prolong thelength of the surgical procedure. If the material experiences atemperature change while hardening, the increase in temperature shouldbe small and the heat generated should not damage the surroundingtissue. The viscosity or fluidity of the material should balance theneed for the substance to remain at the site of its introduction intothe disc, with the ability of the surgeon to manipulate its placement,and with the need to assure complete filling of the intradiscal space orvoids.

Regardless of the injectable scaffold material used, it is critical thatthe completed procedure restore the disc height. It is thus importantthat the proper disc height be maintained while the biomaterial is beingintroduced into the intradiscal space. Ideally, the disc height will berestored to levels equivalent to the heights of the adjacent discs andrepresentative of a normal spinal disc height for the particularpatient.

However, if disc height is not re-established prior to introduction ofthe scaffold material, it will become impossible to replace the lostdisc volume and at least restore the disc height to what it was prior tothe discectomy. Failure to hold a proper disc height as the biomaterialis introduced and cured in situ can eventually lead to a collapse of thedisc space. This phenomenon is illustrated by a comparison of a properintervertebral disc height in FIG. 1 a versus a reduced disc height inFIG. 1 b. The reduced disc height of FIG. 1 b will ordinarily follow asubstantially complete discectomy, unless the adjacent vertebrae aredistracted. The patient can be placed in certain positions that tend toopen the disc space, particularly at the posterior side of the disc D.However, it has been found that even with hyper-flexion of the spine theintervertebral space does not approach its proper volume, andconsequently the intervertebral height does not approach the proper discheight of FIG. 1 a.

Prior procedures for the implantation of a curable disc prosthesis haverelied upon the physical positioning of the patient or upon pressurizedinjection of the biomaterial to obtain some degree of distraction.However, these prior approaches do not achieve repeatable restoration ofproper anatomical disc height, either during the surgical procedure orafterwards. Consequently, there remains a need for a method and systemthat provides a high degree of assurance that a proper disc height willbe established and maintained when the intervertebral disc is replacedor augmented by an injectable biomaterial.

SUMMARY OF THE INVENTION

In order to address the unresolved needs of prior spinal procedures, thepresent invention contemplates a method for injecting a fluent materialinto a disc space. The method includes the steps of creating a portal inthe annulus pulposus in communication with the intradiscal space andimpacting a cannulated distractor into the portal. In accordance withone feature of the invention, the distractor is configured to distractthe vertebrae adjacent the intradiscal space and to establish a discspace height between the adjacent vertebrae. The method includes thefurther step of introducing the fluent material into the intradiscalspace through a lumen of the cannulated distractor while the distractormaintains the established disc space height.

In certain embodiments, the inventive method includes the step ofperforming a discectomy after the portal is created, in which thediscectomy forms a cavity within the intradiscal space. In thisembodiment, the step of impacting a cannulated distractor includespositioning the distractor so that the lumen is in communication withthe cavity, and the step of introducing the fluid includes introducingthe fluid into the cavity. The discectomy can be a total discectomy inwhich substantially all of the nucleus pulposus is removed from the discspace.

In a further feature of the invention, the fluent material is a curablebiomaterial that is particularly suited as a disc replacement oraugmentation material. In this case, the step of introducing the fluentmaterial can include maintaining the distractor in its impacted positionuntil the biomaterial cures in situ. In other words, the cannulateddistractor maintains the adjacent vertebrae in their distracted positionuntil the biomaterial has set. In this way, the proper disc height canbe maintained and retained once the biomaterial has set and thedistractor removed.

In certain embodiments, the fluent material can be introduced into thedisc cavity under pressure. In another feature of the invention that isparticularly useful where the fluent material is under pressure, thecannulated distractor is configured to seal the portal when thedistractor is impacted therein. In some embodiments, the distractor hasa portion sized to substantially block or seal the annular portal. Inother embodiments, the distractor includes a sealing feature that bearsagainst the adjacent vertebrae and/or the annulus fibrosus materialsurrounding the portal. The sealing feature can be integral with thecannulated distractor or can include a separate component, such as aseal ring, mounted on the distractor.

In still another aspect of the invention, and again one that isparticularly suited where the fluent material is under pressure, a ventis provided in the cannulated distractor. Thus, the fluent material canbe introduced into the intradiscal space until the fluent material seepsfrom the vent. Thus, the vent can provide an immediate indication thatthe disc cavity is full.

In some embodiments of the invention, the cannulated distractor isengaged to a fluid injector apparatus. This apparatus can be in avariety of forms, including a pump, a syringe and a gravity feed system.

In other embodiments, the step of introducing the fluent materialincludes extending an tube through the lumen in the cannulateddistractor, with the tube fluidly connected to a source of the fluentmaterial. The tube can be manipulated through the distractor lumen todirect the fluent material to specific locations within the disc cavity.For instance, the tube can be moved through a seeping motion so that thefluent material is completely dispersed throughout the disc space. Atthe same time, the tube can be gradually withdrawn from the distractorlumen as the fluent material nears the lumen opening.

In a preferred embodiment, a seal is provided between the tube and thelumen. A vent can then be provided separate from the lumen so that thefluent material can seep from the vent to indicate that the cavity isfull.

In another embodiment of the invention, a device for injecting a fluentmaterial into a disc space comprises a distraction member havingopposite surfaces configured to distract adjacent vertebrae to the discspace. The distraction member has a proximal end and a distal endportion, in which at least the distal end portion configured to bedisposed within the disc space. The distraction member further defines afluid passageway between the proximal end and the distal end portion,the passageway having an opening at the proximal end and at the distalend portion. In some embodiments, the distraction member can include afitting associated with the proximal end of the distraction member forfluidly connecting the distraction member to a source of the fluentmaterial.

In accordance with another aspect of the invention, the device furthercomprises an elongated cannula defining a lumen therethrough. Thecannula can have a first fitting at one end thereof configured for fluidtight connection to the fitting of the distraction member, and a secondfitting at an opposite end thereof configured for fluid connection to asource of the fluent material. In specific embodiments, the distractionmember is integral with the cannula and the second fitting is thefitting associated with the proximal end of the distraction member. Inother embodiments, the distraction member is removable from the cannula.

In a preferred embodiment, at least the distal end portion of thedistraction member is bullet-shaped. In alternative embodiments, thedistal end portion of is wedge-shaped with opposite substantially flatsides, cruciate-shaped, I-beam shaped and C-shaped.

The fluid passageway of the distraction member includes a central lumenwith a number of openings communicating therewith. The openings can bearranged in the variously shaped distal end portion to direct the fluentmaterial to appropriate locations within the disc cavity. Thedistraction member can also define a vent opening separate from thefluid passageway. In certain embodiments, the fluid passageway can be inthe form of interconnected interstices throughout the distraction membermaterial.

In the preferred embodiment, the distraction member is formed of abiocompatible material, such as stainless steel or titanium. Inalternative embodiments, other biocompatible materials can be used, suchas polymeric materials and even bioresorbable materials. In accordancewith one aspect, the distraction member is configured to be removed fromthe disc space once the fluent material has been introduced into thedisc cavity, and has cured, if necessary. In other aspects, thedistraction member is configured to remain within the disc space, mostpreferably if the member is formed of a bioresorbable material.

The distraction member can include a sealing element associated with aproximal portion of the distal end portion, wherein the sealing elementis configured to provide a substantially fluid-tight seal within thedisc space. The sealing element can include a number of seal ringsdisposed on the distal end portion. The seal rings can be integral withthe distal end portion or can be elastomeric rings mounted on the distalend portion, for example.

It is one object of the invention to provide a system and device formaintaining and enforcing a proper intervertebral spacing or disc heightwhen a disc prosthesis is introduced into a cavity within theintradiscal space. Another object is achieved by features of theinvention that allow introduction of a fluent material into the discspace while maintaining the adjacent vertebrae distracted and the discheight intact.

Other objects and certain benefits of the invention can be discernedfrom the following written description and accompanying figures.

DESCRIPTION OF THE FIGURES

FIGS. 1 a-1 b are lateral views of a disc and adjacent vertebrae showinga proper intervertebral disc height (FIG. 1 a) and a reduced disc height(FIG. 1 b) following a substantially complete discectomy.

FIG. 2 is a lateral view a disc and adjacent vertebrae with a guide wireplaced in accordance with one aspect of the present invention.

FIG. 3 is a sagittal view of the disc space shown in FIG. 2 with atrephine forming a portal in the annulus fibrosus of the disc.

FIG. 4 is a sagittal view of the disc space shown in FIG. 3 with atissue extraction device positioned within the nucleus pulposus of thedisc.

FIG. 5 is a sagittal view of the disc space shown in FIGS. 2-4 with acannulated distractor in accordance with one embodiment of the presentinvention.

FIG. 6 is a side view of a cannulated distractor in accordance with oneembodiment of the present invention.

FIG. 7 is a lateral view of the disc space shown in FIGS. 2-5 with thecannulated distractor of FIG. 6 positioned within the disc space.

FIG. 8 is a perspective view of a distraction tip forming part of thecannulated distractor shown in FIGS. 6 and 7.

FIG. 9 is a perspective view of a distraction tip according analternative embodiment of the invention.

FIG. 10 is a side view of an injector apparatus for use in oneembodiment of the invention.

FIG. 11 is lateral view of a disc space with a cannulated distractor inaccordance with a further embodiment of the invention.

FIG. 12 is a cross-sectional view of a cruciate distraction tipaccording to one embodiment of the cannulated distractor of the presentinvention.

FIG. 13 is a cross-sectional view of an I-beam shaped distraction tipaccording to another embodiment of the cannulated distractor of thepresent invention.

FIG. 14 is a cross-sectional view of a C-shaped distraction tipaccording to a further embodiment of the cannulated distractor of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

The present invention contemplates a procedure and device that isimplemented following removal of a portion or substantially all of thenatural nucleus pulposus of an intervertebral disc. One importantpurpose of the invention is to maintain the proper disc height duringthe introduction of a biomaterial that is intended to replace theremoved nuclear material. Removal of disc material can be accomplishedchemically, such as by the use of Chymopapain. However, the more commonapproach is by discectomy, which can be conducted as an open surgicalprocedure, via microscope-assisted visualization, or throughpercutaneous access.

A typical percutaneous discectomy procedure is illustrated in FIGS. 2-4.In the first step, a guide wire G is directed into an affected disc Dbetween two vertebrae, such as the L2 and L3 lumbar vertebrae. As shownin FIG. 3, the guide wire G penetrates the annulus fibrosus A and thenucleus pulposus N, and it preferably anchored at opposite sides of theannulus A. The guide wire G can be positioned and placed under indirectvision, such as fluoroscopy, or stereotactically, or using other knownprocedures for properly orienting the guide wire within the spinal discD. The procedure shown in the figures utilizes a posterior approach,which is preferable for implementation of the present invention. Ofcourse, other approaches may be utilized for the discectomy inaccordance with known surgical procedures. In addition, the accesslocation may be dictated by the location of a fissure or herniation ofthe disc.

A trephine T is advanced over the guide wire and driven through theannulus A, thereby forming a portal into the disc nucleus. As shown inFIG. 4, a tissue removal device R can be advanced through the trephine Tor through a working channel cannula aligned with the disc portal. Thedevice R can then be used to remove all or part of the nucleus N of thedisc D. As depicted in dashed lines in FIG. 4, a second trephine T′ canbe used to create a second annular portal to facilitate complete removalof the nucleus pulposus of the disc. The tissue removal device R can beof a variety of types, such as a rongeur, tissue morcellator, rotaryand/or reciprocating vacuum-assisted cutter, and even a chemicalintroducer to direct a chemical such as Chymopapain into the nuclearspace. Removal of the nucleus leaves a cavity C (see FIG. 5) surroundedby the substantially intact annulus A

The present invention contemplates the introduction of a biomaterialinto the disc cavity C that is capable or restoring disc height andpreferably substantially normal disc function. For instance, any of thebiomaterials discussed above can fill the newly formed cavity. Inaccordance with the preferred embodiment, the biomaterial is a fluidwith an appropriate flowability and/or viscosity. In particular, thebiomaterial must have sufficient flowability to permit relatively easyintroduction into the disc cavity C, but with sufficient viscosity tohold its shape within the disc. Since the material being used to fillthe disc cavity C is a fluid, the present invention provides means forholding a proper disc height as the material flows into the cavity, tothereby ensure that the cavity is filled—i.e., that the volume ofimplant biomaterial is the same as the volume of nucleus pulposusremoved in the discectomy. Moreover, the methods and devices of theinvention provide a means for maintaining the cavity volume as thebiomaterial transforms to its solid state.

Thus, in accordance with one embodiment of the invention, a cannulateddistractor 10 is provided as shown in FIGS. 5-8. The distractor 10includes a distal end 12 that extends into the disc cavity C and aproximal end 14 that is configured to engage a device for injecting thebiomaterial into the disc space. The distractor 10 includes a cannula 11that terminates in a distraction tip 18 at the distal end of the device.A lumen 16 is defined along the entire length of the device from theproximal end 14 to the and through the distraction tip 18. Thedistraction tip 18 is sized to extend through the portal formed in thedisc annulus A (see FIG. 3). The distractor 10 can include a shoulder 20proximal to the distraction tip 18, in which the shoulder is sized toprevent passage through the annular portal. The shoulder 20 can operateto limit the distance that the distraction tip 18 extends into the disccavity C. The distractor 10 can be provided with means for temporarilyfixing the distractor in position or supporting the distractor on theadjacent vertebrae.

As shown in FIG. 7, the distraction tip 18 is intended to be insertedthrough the annular portal and is configured to restore the appropriateintradiscal height in the cavity C. Thus, in one embodiment, thedistraction tip 18 can include a tapered leading portion 24. Thisleading portion 24 can be introduced into the cavity C and as the tip isadvanced further into the cavity the leading portion will graduallydistract the adjacent vertebrae as the leading portion 24 bears againstthe disc endplates E. In a specific embodiment, the tapered portion 24can be substantially bullet-shaped, as shown in FIG. 8. With thisconfiguration, the distraction tip 18 can have any rotationalorientation when the tip is inserted through the annular portal.

Alternatively, the distraction tip can be configured like the tip 40shown in FIG. 9. With this embodiment, the tip includes opposinggenerally flat sides 50 and intermediate edges 52 of the wedge portion42. The tip 40 can be introduced into the disc space with the flat sides50 of the wedge facing the disc endplates E. Once the tip is fullywithin the disc cavity C, the tip can be rotated so that the edges 52contact and distract the endplates. The edges 52 themselves can bewedge-shaped, having a greater width at their proximal end than at theirdistal end.

Returning to FIGS. 6-8, in accordance with one feature of the invention,the distraction tip 18 includes a number of side orifices 30 and an endorifice 32 that all communicate with the central lumen 16. As depictedin FIG. 7, the orifices 30, 32 provide an exit path for fluid injectedthrough the lumen 16. Preferably, the orifices are oriented to beunobstructed by the vertebral endplates E. The distraction tip 40 shownin FIG. 9 is also provided with side orifices 46 in the flat sides 50and an end orifice 48. With this embodiment, the edges 52 need notinclude orifice(s) because the edges will be occluded by contact theendplates.

Since fluid is intended for introduction through the distraction tip 30,it is preferable that some feature be provided to ensure a substantiallyfluid-tight seal at the entrance to the disc cavity C through theannular portal. Thus, in one embodiment of the invention, thedistraction tip 30 can include annular rings 26 that are intended tobear against the disc endplates E and/or the disc annulus A in a sealingrelationship. The rings 26 can be integral with the distraction tip 30,or can be separate components mounted on the distraction tip, such as inthe form of elastomeric seal rings. The seal rings can be mounted withinannular grooves formed in the distraction tip.

The distractor 10 includes a fitting 36 defined at the proximal end 14of the cannula 11. The fitting 36 provides means for making afluid-tight connection with a device adapted to inject the biomaterialinto the disc. One exemplary device 70 is shown in FIG. 10. The injector70 includes a chamber 72 for storage of the biomaterial. In some cases,the chamber 72 may constitute multiple chambers where the injectablebiomaterial is obtained by mixing various constituent materials. Forinstance, certain materials may be curable in situ and may requirecombining a curing agent with a base material. To facilitate mixing ofthe biomaterial constituents, the injector 70 can include a mixingchamber 74. A manual control 76 can be provided that forces the contentsof the chamber 72 into the mixing chamber 74. Alternatively, theinjector 70 can incorporate a mechanism that drives the fluid from theinjector under pressure, such as a syringe or a pump.

The injector 70 includes a fitting 80 that is configured for fluid-tightengagement with the fitting 36 of the cannulated distractor 10. In apreferred embodiment, the two fittings 36, 80 represent matingcomponents of a LUER® fitting. The injector can include a nozzle 78 thatextends into the cannula 11, or more specifically into the lumen 16,when the injector 70 is engaged to the cannulated distractor. A grip 82can be provided to allow manual stabilization of the injector.

As explained above, the cannulated distractor 10 of the presentinvention may be utilized after a discectomy procedure. For purposes ofillustration, it has been assumed that a total discectomy has beenperformed in which substantially all of the nucleus pulposus has beenremoved, leaving a disc cavity C as shown in FIG. 5. Of course, theprinciples of the invention can apply equally well where only a portionof the disc nucleus has been removed through a partial discectomy. If abilateral approach has been used (as represented by the first and secondtrephines T and T′), one of the annular portals can be sealed with amaterial compatible to the disc annulus fibrosus. When the nucleus hasbeen cleared, the guide wire G can be repositioned within the disc D,again preferably using known guidance and positioning instruments andtechniques. The cannulated distractor 10 can then be advanced over theguide wire until the distraction tip 18 is properly situated within thenuclear cavity C. Preferably, the proper depth for the distraction tip18 can be determined by contact of the shoulder 20 with the outerannulus A, or by contact of an associated depth feature with theadjacent vertebral bodies.

With the distraction tip 18, the tapered portion 24 gradually separatesthe adjacent vertebral endplates E as the distraction tip is drivenfurther into the disc space. A mallet, impactor or other suitable drivercan be used to push the tapered portion 24 into position against thenatural tension of the disc annulus. It is understood that the goal ofthis step is to fully distract the intervertebral space to a proper discheight for the particular spinal level. For instance, for the L2-L3 discspace, the appropriate disc height may be 13-15 mm, so that thedistraction tip is positioned within the cavity C to achieve this amountof distraction. As shown in FIG. 5, preferably only one cannulateddistractor 10 is utilized, since the distraction tip 18 necessarilyoccupies a certain portion of the volume of the cavity C. However, asecond cannulated distractor and associated distraction tip may benecessary (such as through a second annular portal as shown in FIG. 4)to achieve the proper disc height.

It should be understood that the process thus far would be similar forthe distraction tip 40. However, unlike the tapered distraction tip 18,the distraction tip 40 requires an additional step to distract the discspace. Specifically, the distraction tip 40 is initially inserted withits flat sides 50 facing the endplates E. The tip must then be rotateduntil the edges 52 bear against and support the endplates. The flatsides 50 can include an angled transition to the edges, or the edges 52can be rounded to facilitate the distraction as the distraction tip isrotated in situ.

When the distraction tip, such as tip 10, is inserted to its properdepth within the disc cavity C, the annular portal is sealed, whether bycontact with the shoulder 20, or by engagement of the rings 26 with theendplates E or the interior of the annular portal. At this point, thebiomaterial fluid can be injected into the cannulated distractor, andspecifically into the lumen 16. To accomplish this step, the injector,such as injector 70, can be mated with the fitting 36 at the proximalend 14 of the cannulated distractor. Optimally, the guide wire G isremoved and the fitting 80 of the injector engages the fitting 36. Thenozzle 78 extends into the lumen 16. The nozzle can be sized so that theexit end of the nozzle is near or within the distraction tip 18. At thispoint, the injector 70 can be actuated in accordance with itsconstruction so that the biomaterial fluid is displaced from theinjector and into the lumen 16. The biomaterial exits through theorifices 30, 32 in the distraction tip 18 to fill the cavity C. Theorifices 30, 32 are preferably positioned and sized to achieve completeand rapid dispersion of the biomaterial throughout the cavity. Again,the goal of this step of the process is to completely fill the entirevolume of the cavity, or to replace the entire volume of nucleuspulposus removed during the discectomy. Where the fluid biomaterial isan in situ curable or settable material, time may also be of the essenceto ensure a homogeneous mass once the material is completely cured.

It should be apparent that the distraction tip 18, 40 maintains theproper disc height while the biomaterial is injected. The tip can beretained in position until the injected material cures or sets. Once thematerial has sufficiently cured, the distraction tip 18, 40 can beremoved. Since the distraction tip occupies a certain volume, additionalbiomaterial can be injected through the tip as it is being withdrawn, ifrequired, thereby filling the gap left by the tip.

In certain embodiments, the distraction tip 18 can be a modular andremovable from the cannula 11, as shown in FIG. 8. Thus, the tip 18 andcannula 11 can be provided with a removable mating element 19, such as apress-fit (as shown in FIG. 9) or a threaded or LUER® type fitting (notshown) as would occur to a person of skill in this art. A removabledistraction tip can serve several purposes. In one purpose, the injectedbiomaterial may require a lengthy curing time. While the material iscuring, it is of course necessary to keep the distraction tip inposition to maintain the proper disc height. However, it may not benecessary to retain the other components of the system in position, suchas the injector 70 and cannula 11. A modular distraction tip allows thecannula 11 to be removed while the tip remains in position, acting as adisc spacer while the biomaterial cures.

In another purpose, a number of differently sized tips can be mounted toa commonly sized cannula. Each patient has a different spinal anatomy,which means the appropriate disc height at a given spinal level may varybetween patients. Moreover, the disc height can vary with spinal level.Thus, a plurality of differently sized distraction tips 18 can beprovided to ensure proper spacing across the spinal disc D.

Another purpose behind a removable distraction tip 18 is achieved byembodiments in which the tip is formed of a biocompatible material thatallows the tip to remain resident within the disc space. In thisembodiment, the distraction tip material must be compatible with thebiomaterial used to replace the natural nucleus. For instance, if thebiomaterial is only intended to restore disc height, but not the naturalbiomechanical properties of the natural nucleus, then the material ofthe distraction tip 18 may provide a generally rigid scaffolding. On theother hand, and most preferably, the injected biomaterial is intended toemulate the biomechanical characteristics of the disc to allow thespinal segment to operate as close to a normal spinal segment aspossible. In this instance, a rigid scaffold would of course frustratethe normal flexion, compression and torsional responses of the disc.Thus, the distraction tip 18 in embodiments where the tip is left insitu can be formed of a biodegradable or bioresorbable material thatabsorbs into the matrix of the cured biomaterial forming the discnucleus prosthesis.

Whether the distraction tip is removed or remains within the disc space,it is preferable that the tip occupy as little volume as possible. Onthe other hand, the distraction tip must be sufficiently strong tosustain the compression loads that it will face while distractingadjacent vertebrae and holding the disc space height while the injectedbiomaterial cures. In the specific embodiments shown in FIGS. 5 and 7,the distraction tip 18 is shown traversing across a substantial portionof the nuclear cavity C. Alternatively, the distraction tip can have areduced length from the shoulder 20 so that the tip extends onlypartially into the cavity. Distraction of the disc space can be abettedby certain positions of the patient on the operating table where, forinstance, the anterior aspect of the disc space is naturally distractedby the position of the spine. Proper distraction of the disc space maybe better accommodated by an anterior approach, rather than theposterior approach shown in FIGS. 5 and 7.

In alternative embodiments, the distraction tip can assume a wide rangeof geometries, some dictated by the annular portal formed during thediscectomy procedure. In the embodiment of FIGS. 5-8, a circular annularportal has bee created and a circular distraction tip 18 utilized toseal the portal. In some cases, a planar or wedge-shaped distractiontip, similar to the tip 40 shown in FIG. 9, can be utilized where theopening through the annulus has an area greater than the tip itself. Inthese cases, the extra space between the tip and the interior surface ofthe portal can provide an opening for a direct visualization instrument,or some other appropriate instrument. Preferably, this approach isbetter suited where the biomaterial is not injected under pressure, suchas cases where a gravity feed is employed (see FIG. 11 and associateddiscussion below).

In other cases, surgeons perform the discectomy through rectangular orcruciate portals in the disc annulus. A complementary shaped distractiontip can be utilized to conform to and fill the annular portal. Forinstance, the distraction tip can assume the configuration shown inFIGS. 12-14. A cruciate-shaped tip 55 is shown in FIG. 12 with a centrallumen 56 communicating with a number of openings 56. It is understoodthat the arms of the cruciate-shaped tip can have a thinnercross-section than shown in the figure, provided they are sufficientlystrong to support the adjacent vertebrae in their proper distractedposition. Likewise, the openings 56 can be distributed in a variety ofpatterns through the hub and legs of the cruciate shape.

An I-beam distraction tip 60 is shown in FIG. 13 having a central lumen61 communicating with a number of openings 62. The distraction tip 63 inFIG. 14 has a C shape and includes a lumen 64 and openings 65. These twobeam configurations provide sufficient support for the necessarydistraction. Again, the thickness of the arms of the beams can bereduced as necessary to minimize the cross-section of the distractiontip 60, 63.

Regardless of the overall configuration of the distraction tip, it ismost preferable that volume of the tip within the nuclear cavity C beminimized. The bullet-shaped tip, such as tip 18, may be less desirablefrom that standpoint, while the wedge type, such as tip 40, may bepreferable. In addition, regardless of the overall configuration, thedistraction tip must communicate with the lumen 16 and must provide somemeans for discharge of the biomaterial fluid through the tip. In theillustrated embodiments, the distraction tips 18, 40 include orifices30, 31 and 46, 48, respectively, that communicate with the correspondinglumens 16, 44. Alternatively, the distraction tips can be in the form ofan open scaffold or skeletal framework. Again, the scaffold or frameworkmust be sufficiently strong, especially in compression, to properlydistract the disc space and hold the disc height for an appropriatelength of time. In some embodiments, the distraction tip can be formedof a material having interconnected interstices, such as a porousmaterial. The porous distraction tip can present a solid scaffold with amultitude of fluid flow paths through the material. The porous materialcan be a metal, such as a porous tantalum; however, a porous polymer,such as polylactic acid, is preferred so that the scaffold does notobscure visualization of the disc space after the procedure iscompleted.

In the procedures discussed above, the distraction tip has beendescribed as providing an avenue for the injection of a biomaterial intothe nuclear cavity C following a discectomy procedure. The distractiontips of the present invention serve equally well as a conduit for theintroduction of other fluids to the disc space. For instance, thedistraction tips can be used to inject a biomaterial such as thematerial disclosed in provisional application Serial No. 60/336,332,entitled “Pretreatment of Cartilaginous Endplates Prior to Treatment ofthe Intervertebral Disc with an Injectable Biomaterial”, mentionedabove, the disclosure of which is incorporated herein by reference. Thisprovisional application discloses materials for the pretreatment of thedisc endplates, for instance, to improve the biological functioning of adegenerative disc. The cannulated distractors of the present invention,such as distractor 10, can be initially used for the disc pretreatmentsdisclosed in the above-mentioned provisional application. Once thepretreatment has been completed, the cannulated distractor can then beused for the injection of the curable biomaterial.

Likewise, the present inventive cannulated distractor can be used formultiple fluid injections, including multiple injections to effectcuring of a biomaterial within the nuclear cavity C. For instance,certain biomaterials may include a first constituent that is introducedinto the disc space, followed by a second constituent or curing agent.The second constituent can initiate curing of the resulting composition.

An alternative embodiment of the invention is depicted in FIG. 11. Inthis embodiment, a cannulated distractor 85 is provided that includes agenerally frusto-conical distraction tip 86 and a shoulder 87. The tip86 is configured to act as a wedge to distract the disc space as thecannulated distractor 86 is impacted into the disc space. The shoulder87 acts as a stop against the adjacent vertebral bodies to limit thedistance that the tip is driven into the disc space. Preferably, thedistraction tip 86 has a length from the shoulder 87 to its distal endthat is sufficient to span the length of the portal in the disc annulusA, but is limited in its extent into the nuclear cavity C. With thisembodiment, the distraction tip 86 does not displace any significantvolume within the cavity C.

The cannulated distractor 85 defines a lumen 88 extending the entirelength of the distractor. The lumen 88 is sized to receive an injectiontube 94 therethrough. The injection tube 94 can include a fitting 96 forengaging an injection apparatus 98. The fitting 96 can be of anysuitable type, such as the LUER® fitting mentioned above. The injectionapparatus can be similar to the injector 70 shown in FIG. 10, or canassume a variety of configurations for the introduction of a fluid intothe disc cavity. In one embodiment of the invention, the biomaterialfluid is introduced into the cavity by way of gravity feed. In thisinstance, the injection apparatus 98 can be simply in the form of areservoir with an atmospheric vent to allow the biomaterial to flowdownward into the disc space by gravity alone. Of course, the patientmust be properly presented to accommodate gravity filling of the disccavity C.

In this embodiment, the cannulated distractor 85 operates as a supportor guide for the injection tube 94. The tube 94 can be in the form of asmooth tipped, relatively large gauge needle that is sized toaccommodate optimum flow of the biomaterial into the disc space. Thetube 94 can be introduced through and gradually withdrawn from thecannulated distractor 85 (as indicated by the arrow in FIG. 11) as thebiomaterial flows into the cavity C. In addition, the diameter of thetube 94 can be sized relative to the diameter of the lumen 88 so thatthe discharge opening 95 of the tube 94 can be pivoted with a sweepingmotion through the cavity C. This aspect of this embodiment facilitatescomplete direct filling of the disc cavity C with the biomaterial. Wherethe cannulated distractor is used to introduce pre-treatment materials,such as those discussed above, this feature allows positioning of thedischarge opening 95 to direct the pre-treatment materials where theyare needed.

In certain embodiments, the lumen 88 can be provided with a seal 89,which can be in the form of an elastomeric seal ring. The seal 89 canform a fluid-tight seal around the injection tube 94, which can beespecially important where the biomaterial is injected under pressure.In addition, the seal 89 can operate as a form of joint to support theinjection tube 94 as the discharge opening 95 is manipulated within thedisc cavity.

In another feature of the invention, the cannulated distractor canprovide a vent for the discharge of excess biomaterial when the disccavity C is full. The vent is particularly useful where the biomaterialis introduced under gravity feed. In one specific embodiment, a venthole 92 is provided in the distractor 85. When the disc cavity is full,the biomaterial will seep through the vent opening 92, providing adirect visual indication that the cavity is full. Preferably, the ventopening 92 includes a tube that projects away from the cannulateddistractor 85 to improve the visibility of the vent in situ.Alternatively, the vent can be formed by a difference in diameterbetween the injection tube 94 and the lumen 88, and in the absence ofthe seal 89.

The vent 92 is well-suited to procedures involving gravity feed of thebiomaterial into the disc space. However, the vent can also be usefulwhere the material is fed under pressure. For example, the vent 92 canbe maintained initially open as the biomaterial is injected into thecavity C through the injection tube 94. When the cavity is completelyfull, biomaterial will seep from the vent 92. As this point, the ventcan be closed and additional biomaterial injected into the disc space toincrease the pressure within the cavity C. The seeping through the ventprovides an immediate indication that the cavity is full, and canprovide a starting point for the introduction of a calibrated amount ofadditional biomaterial to achieve a proper cavity pressure.

With each of the embodiments, once the biomaterial has cured and thecannulated distractor removed, the portal or portals in the disc annuluscan be filled to prevent herniation of the newly formed prosthetic discmaterial. The annular portal can be sealed with any suitable material,such as fibrin glue, or a polymerizable material, or the like. Thematerial used to seal the annulus should be sufficiently strong toremain intact as the intradiscal pressure is increased due to hydrationor biomechanical movement of the spine.

In accordance with certain embodiments, the cannulated distractors, andparticularly the distraction tips, described above can be formed avariety of bio-compatible materials. As explained above the distractiontips must be sufficient strong to maintain proper distraction of thedisc space until the biomaterial has been fully injected and cured, ifnecessary. In certain embodiments, the distraction tips are formed of abio-compatible metal, such as stainless steel or titanium. In otherembodiments, the distraction tips are formed of a polymer or plasticthat is preferably radiolucent to permit visualization of thedistraction tip in situ to verify the position of the component.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

1. A kit of parts for sealably introducing fluent material directly intothe disc space having a height between opposed vertebrae through anopening extending through the annulus fibrosis of said disc forreplacing nucleus pulposus, comprising: a tube having a passageway forthe flow of fluent material therethrough and an extent adapted to bereceived in the opening of said annulus fibrosis, said tube having aseal adapted to engage said annulus fibrosis adjacent said opening andto form a fluid-tight seal therewith, wherein said tube extent isdefined by a distal tip of said tube, said distal tip having a dimensiongreater than the height of said disc space that is sized and configuredto provide distraction of opposed vertebrae communicating with said discspace; and a quantity of curable fluent material adapted to beintroduced in a fluid state into said disc space through the passagewayof said tube, said material upon curing having properties substitutiveof the nucleus pulposus.
 2. The kit of parts according to claim 1,wherein said seal is integral with said tube.
 3. The kit of partsaccording to claim 1, wherein said seal is a separate component mountedon said tube.
 4. The kit of parts according to claim 1, wherein saidfluent material is a curable biomaterial selected from the group ofnucleus pulposus substitutes consisting of hyaluronic acid, fibrin glue,alginates, elastin copolymers and collagen gels.
 5. The kit of partsaccording to claim 1, wherein said distal tip comprises at least oneorifice communicating with said passageway to provide an exit path forsaid fluent material into said disc space.
 6. The kit of parts accordingto claim 1, wherein said distal tip is removable from said tube.
 7. Thekit of parts according to claim 6, wherein there are a plurality ofremovable distal tips, each being of different size.
 8. The kit of partsaccording to claim 6, wherein said distal tip is formed of bioresorbablematerial.
 9. The kit of parts according to claim 1, further including asyringe adapted to inject said fluent material into the passageway ofsaid tube.
 10. The kit of parts of claim 1, wherein said seal is adaptedto reside within said opening of said annulus fibrosis.
 11. The kit ofparts according to claim 1, further including an injector adapted to becoupled to said tube for injecting said fluent material into said tubeunder pressure.
 12. The kit of parts according to claim 11, wherein saidinjector includes a syringe.
 13. The kit of parts according to claim 11,wherein said injector includes a pump.
 14. The kit of parts according toclaim 11, wherein said injector includes a mixing chamber.